The long-term objectives of this application are to learn more about how chromatin structure controls transcription initiation in eukaryotic cells. Histones and other functions that have been shown to be important in yeast are conserved in other eukaryotes, including humans. These functions include the SNF/SWI complex, required to overcome transcriptional repression by nucleosomes. The studies will focus on three related areas that concern how RNA polymerase II transcription initiation is controlled by factors that modulate chromatin structure. In all three areas, both genetic and biochemical approaches will be taken. First, histone mutants that alter transcription in vivo will be analyzed. Previously studied histone H2A mutants will be analyzed by identifying nonhistone proteins with which this histone interacts, as well as by biochemical analysis of nucleosomes that contain this mutant histone. Mutations in genes that encode histones H2B, H3, and H4 will also be identified and analyzed. Second, the SPT4/SPT5/SPT6 complex, required for repression by nucleosomes in vivo, will be studied both in vivo and in vitro. These analyses will include defining the interaction between the SPT6 protein and histones, the purification and analysis of the SPT4/SPT5/SPT6 complex, and study of the human homologue of SPT4. Third, the SUC2 promoter, strongly controlled by the SNF/SWI complex, will be analyzed in detail to determine the cis- acting elements and the trans-acting factors that are required for SNF/SWI control. These studies should reveal important aspects of how chromatin structure controls transcription initiation in yeast. Since histones, SNF/SWI, and SPT4/SPT5/SPT6 are all conserved, these studies will be directly applicable to understanding transcription in other eukaryotes, including humans. Since altered transcription in humans has been implicated in diseases such as cancer, these studies are relevant to human disease.